This invention relates to ethylene-propylene-diene ionic elastomer compositions useful for fabricating products by injection molding, extrusion and other processing techniques wherein the said ionic polymeric compositions have improved impact resistance and modulus and more specifically to ionic elastomeric polymeric compositions comprising an ionic polymer and poly(alpha-methylstyrene).
In general, ionic polymers have a covalent bonded backbone such as are produced from polymerizing ethylene, propylene, vinyl acetate, vinyl methyl methacrylate, or substituted and unsubstituted styrene. From this backbone, there are pendent carboxyl or sulfonic acid groups which have cations such as zinc, sodium, cesium, etc., substituted for some portion of these acids. These ionic interchain forces clustered between the long chain molecules of the polymer structure give ionomer resins of the several monomers used solid state properties normally associated with a cross-linked structure.
Polymeric ionic compositions useful for fabricating products by injection molding or extrusion methods or other thermal methods useful in plastics processing can range in properties from those that match flexible vinyl to vulcanized rubbers according to the monomer and formulation used. Some ionic polymers are flexible like rubber and can be processed like thermoplastics.
The properties of ionic polymers relate to the presence of ionic groups. At low temperatures, the ionic groups of ionic polymers attach to each other in clusters called ionic domains. These domains connect the molecules of the polymer in such manner that the materials have strength and flexibility. Since the connecting or cross-linking of the domains is by ionic rather than by covalent bonding between the molecules, the ionic bonding permits the polymer to be deformed and worked in the same manner as thermoplastic resins upon the application of heat.
It is generally believed that cross-linking occurs through ionic domains which are made up of the partially neutralized pendent acid groups interacting between chains. This linking is reversible by heating and cooling. Once these domains are disrupted, the polymers can be compression or injection molded. The ease of filling a mold is primarily a function of melt viscosity. The lower the melt viscosity or the higher the melt flow, the easier the molten polymer can be made to fill a mold.
Although the ionic bonding accordingly permits obvious advantages in processing of thermoplastic resins, ionic polymers typically suffer from the problem of being more difficult to process than similar polymers with covalent rather than ionic bonding.
The ionic polymers or ionomers are prepared by a variety of techniques using numerous homo, co- and terpolymers as backbones. However, while all ionomers have several obvious advantages, one characteristic problem common to all is the difficulty of modifying the physical characteristics of the monomers as compared to similar polymers having the same backbone but without the ionic cross-linking.
The use of preferential plasticizers, i.e., plasticizers which primarily relax ionic bonds, are taught in the prior art as in U.S. Pat. No. 3,847,854 for improving the processability of ionic hydrocarbon polymer compositions. However, preferential plasticizers are not disclosed as affecting the properties of the polymers at normal use temperatures since the non-volatile plasticizers remaining in the final product act essentially as inert fillers and the volatile plasticizers are evolved from the ionomer once they have performed their function.
It is a general object of this invention to provide improved compositions of polyolefin ionic polymers wherein the physical characteristics can be modified and the resulting polymers have improved processability.
It has now been unexpectedly discovered that it is possible to prepare compositions of polyolefin ionic polymers which have modified and improved physical characteristics. These compositions comprise a thermoplastic polyolefin ionic polymer and poly(alpha-methylstyrene). The resulting compositions are physical mixtures, the individual components of which are linked together by various intermolecular forces, such as Van der Waal's forces, dipole-dipole interactions, or hydrogen bonding, or by chain entanglement. Thus, these systems differ sharply from block or graft copolymers in which the bonding between various components is covalent in nature. As is generally known, in contrast with low molecular weight substances, few polymers are miscible in the absence of specific polymer-polymer interaction. Phase separation is a general consequence of incompatibility. Improved performance characteristics such as improved mechanical dynamic tests without phase separation indicate compatibility of components.
The compositions of this invention differ from plasticized polyolefin polymers in that plasticization provides improved processability of the polymer at lower temperatures whereas the compositions of this invention can improve performance characteristics without necessarily improving the processability of the resulting product such as reducing processing temperatures or workability.